Police said Harper shot Mariah Anderson, 22, after she was escorted to her car by a coworker outside a Walmart in Union Township, near New Castle, on Sunday night.

Investigators say Anderson had just finished her shift at the store and was driving away in her SUV when several shots were fired into the vehicle at about 11:15 p.m. Anderson died on the way to the hospital.

"There is some video from Walmart and some witness interviews that were done that led us to the suspect," Lt. Eric Hermick said.

After police arrived at the home in New Brighton about 8 a.m. Monday, they said one shot was fired from inside the residence, and one round did come outside. No shots were fired by police.

Police said Harper put many people in danger. “This is a housing complex with multiple buildings around it, multiple apartments adjacent to it, wood floors. There was just a hellacious amount of danger for the kids getting up for school this morning. The weapon that was used at New Castle in Union Township was a .40-caliber semiautomatic handgun. We assume that is the weapon he has in his possession at this time," Hermick said. "All we know is he posed a question ... asked one of the persons inside the residence to see if they could look outside and see if police were outside. We believe he is aware that we are looking for him, and when he was told that, that's when a shot was fired that went out the window."

Anderson had three children, ages 1, 3, and 4, according to her sister, who also said that Anderson had recently broken up with the father of her children. She said that Anderson had filed for a protection-from-abuse order, and that police had taken the man away from the store a couple of times before Sunday.

"Every day, he'll be at her job, sitting out, waiting for her to get off so he could follow her. Every day, she would have to call the police," Anderson's sister said. "It got to the point where he was hiding in her trunk of her car and just following her around from work and having people go to her job, watching her, things of that nature."

A criminal complaint was filed Wednesday against Harper, and it lists charges of simple assault (domestic violence), false imprisonment, indecent assault and harassment. Anderson is identified as the victim in that incident, which happened at her home, according to the paperwork.

“Due process is maybe what kept him out, I don’t know," said Lt. Hermick. "He was also a drug trafficking target of our agency. We were working to apprehend him working under cover through drug purchasing.”

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